Do have any pictures? Measure the box. That will help give an idea of the model. They came in 8ft, 10ft, 12ft, and back then they even had a 14ft with dual axles. I think they even had a 6ft at one time.
2013 Jayco Jayfeather X20 E, 2008 GMC Sierra 1500 Crew Cab Z71 SLE